Effect of Film Thickness on Induction Time of Isothermal Crystallization from the Melt of Poly(3-hydroxybutyrate) Investigated by Time-resolved Grazing-incidence X-ray Scattering Measurements Using Synchrotron Radiation

Abstract

Isothermal crystallization behaviors from the melt have been investigated for poly (3-hydroxybutyrate) (P3HB) thin films by time-resolved measurements of grazing-incidence X-ray scattering using synchrotron radiation. P3HB films with thicknesses of ca. 25 nm ~ 3.2 μm prepared on silicon substrates were cooled rapidly from the melt to a crystallization temperature, Tc, of 373 K by using a temperature-jump (T-jump) apparatus. Isothermal crystallization behaviors of P3HB in thin films were traced by simultaneous measurements of grazing-incidence wide-angle X-ray scattering (GIWAXS) and small-angle X-ray scattering (GISAXS). It was experimentally found for the first time that the induction time of crystallization became longer with reducing the film thickness. This indicated that the chain mobility necessary for nucleation at 373 K was reduced in thin films. It was also indicated that lamellar crystals having the edge-on type orientation to the substrate surface were preferentially formed at the beginning of crystallization. Those lamellae in the thin films might be stacked one another with amorphous chains in a disordered manner.